When the living segment is ingested by another primary host, the proglottids regenerate a new scolex, which attaches itself to the intestinal wall, and the tapeworm resumes its growth by budding. When eggs are ingested, they hatch in the intestinal tract and release larval forms, which burrow into the tissues of the host and form cysts (see Cyst). These encysted forms are known by such names as bladder worms, cycticerci, hydatids, and measles; the host harboring this stage is known as an intermediate host, in contrast to the primary host, in which the tapeworm seeks the alimentary canal and develops there. The larvae often exhibit specific selection of tissues in encysting; for example, one species attacks the liver in humans and dogs, whereas another attacks the brain in sheep, causing the disease known as gid or staggers. When larvae are ingested by a primary host, usually in the form of encysted meat of the intermediate host, they are stimulated by the gastric juice to develop into adult tapeworms. The adults attach themselves to the intestinal wall and absorb partially digested food through their body surface; tapeworms have no mouths or digestive canals.
Several vermifuges, poisonous worm-killing substances, are effective in proper dosages in treating tapeworm infestation. Unless the scolex is dislodged, the worm is not eradicated.
up the class Cestoda. The tapeworm larva that attacks the liver in humans
and dogs is classified as Taenia echinococcus. The tapeworm larva
that attacks the brain in sheep is classified as Taenia coenurus.